If often argue with people over the merit of sutemiwaza (I've probably argued with Kit about it before!), all the comments relating to the ground being a bad place to be in real combatives are correct, you don't want to go there! But, if you're going anyway, isn't it nice to take your attacker with you, especially if you can make sure he hits the ground harder than you, and usually you make him lead with his head!
I see sutemiwaza as a changing technique, he has off-balanced you, it may even be that he has thrown you, but it's not perfect and he gives you room to position yourself, as you break your fall, you are off-balancing him and his arc to the ground is much shorter, he's not expecting it, splat.
Most of the rolling falls you see from sutemiwaza are there purely because we are being nice to our partner, the actual technique (to me anyway) should involve you accelerating his head into the ground, and often you do it with his full body weight and your added force behind it.
Take stomach throw, tomoenage, for example, we train and are taught to stick the foot into the lower abdomen, hold his arms or shoulders and as we roll under him, push with the leg and pull with the arms. In many styles they let go so he can sail away spectacularly, we tend to hold on so we can continue the roll and end up on top. But imagine if you don't push too hard with your leg, once he's moving you push with your arms instead, now he's airbourne, still in your control but he can't tuck his head and roll, his face, or the top of his head contacts with the ground and because of the body weight thing, his neck likely breaks. DON'T TRY THIS AT HOME!!!
I don't advocate the use of sutemiwaza as a initial defence, but it is an effective changing technique and does have a place in the jujutsu arsenal, maybe somewhere down the back in the shadows.
Regards
Neil
Neil Hawkins
"The one thing that must be learnt but
cannot be taught is understanding"